Paper coating composition, paper coated therewith, and method of improving the strength of paper



PAPER COATING COMPOSITION, PAPER COATED THEREWITH, AND METHOD OF IMPROVING THE STRENGTH OF PAPER John T. Moynihan, Hyattsville, Md., assignor to the United States of America as represented by the Secretary of Commerce I No Drawing. Application March so, 1953 Serial No. 345,743

The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of 35 US. Code, Section 266.

p The present invention relates toa method of, and a tubsizing solution for, treating cellulose compounds and in particular'to a method of and solution for treating currency paper to improve vthe elasticity and resistance to crumpling of said paper. Currency and bank note papers in all nations of the world wear out rather quickly because of frequent folding, crumpling, and exposure to dirt and grease during handling. Since such papers are used in large quantities in the principal commercial nations, and since the engraving and printing process is quite expensive,,any feasible method of extending the life of the paper would result in substantial economy to the governments concerned. In the history of papermaking through the centuries, some improvements in strength have been effected by changes in the methods of cooking, beating, and refining the pulp, and by addition of wet-strength resins to the pulp before the paper is made. Strength can also be improved slightly by tub-sizing with glue or resins, but this process changes the flexibility, absorptiveness. and surface characteristics of the paper by depositing a surface coatmg.

In the prior art it was known that by plasticizing paper its flexibility could be increased, but at the same time the tensile strength was decreased. On the other hand when resins alone were used the tensile strength of the paper 'was increased but the flexibility was decreased. It is therefore the primary object of the invention to provide a method of and solution for treating cellulose compounds so as to increase both the tensile strength and the flexibility of the compounds.

Another object of the present invention is to provide a method of and bath for treating paper which increases the resistance of the paper to deterioration due to crumpling.

Another object of the invention is to provide a method of and solution for treating paper which makes the paper substantially impervious to oil penetration.

, 'Another object of the present invention is to provide a method of and solution for treating paper which increases the elasticity of the paper.

Another object of the present invention is to provide a method of and bath for treating paper which improves the pick-test characteristics of the paper.

Another object of the present invention is to provide a method of and bath for treating paper which produces the above-desired results without affecting the tearing strength'or'we t tensile strength of the paper.

Another object of the present invention is to provide a method for increasing the-tensile strength and flexibility or paper by treating it with. a composition containing a resin and aplasticizer in an'aqueous medium.

States Pare Another object of the present invention is to provide a method of increasing the flexibility, the resistance to crumpling, the folding endurance, and the tensile strength of paper by treating it with a composition containing a water soluble resin and a plasticizer chosen from one of the water soluble polyhydric alcohols.

A further object of the invention is to provide a paper which has a high tensile strength and a high degree of flexibility. t

Specifically the composition for treating the paper consists of urea-formaldehyde and a plasticizer. The plasticizer used is chosen from the water-soluble polyhydric alcohols, specifically, glycerol, sorbitol, and mannitol. A water-soluble compound as used herein is meant to mean any one of the afore-mentioned substances which will form a true solution with water or which will form a colloidal solution with water.

In the present invention the tub-sizing solution used is made up of 15-20 percent by weight glycerol as a plasticizer, 10-15 percent by weight urea-formaldehyde, and the remainder water. To obtain a solution which produces a very good and extremely penetrating dispersion of the resin among the dense fibers of the paper, the glycerol and water are mixedand then a solution of 30-35 percent urea-formaldehyde in water is added to the glycerol-water solution while the solution is rapidly stirred.

After treatment the paper is dried at degrees centigrade from 2 to 4 minutes. However, the temperatures can be varied over wide limits, the lower limit being about 60 degrees C. and the upper limit depending upon the highest temperature to which the paper and/or resin could be subjected without deterioration. The temperature employed for a particular operation dependsupon the final properties of the paper which are desired.' The time of drying depends upon the temperature to which the paper is subjected, the paper and resin used, and the type of furnace employed for drying A web of paper can be continuously run through the sizing solution and then through a dryer. Table No. 1 indicates the percentage of each material in the preferred sizing solution and the percentage of each material retained in the paper after treatment. The amount of the material retainedin the paper depends upon the percentage of each material present in the sizing solution and the absorptive qualities of the paper. However, on an average the paper will retain approximately 3-4 percent by total weight of the paper of resin and 7-9 percent plasticizer.

TABLE 1 Mill-run analysis Tub Goncentratlons (Percent) Retention (Percent) Glycer I Water 73 4-7 on the Massachusetts Institute of Technologyfoldiirgendurance tester. Crumpling endurance was" measured by a procedure suggested by Carson and Worthington in which the paper is reproducibly crumpled and its deterioration measured by an air permeability tester which determines the amount of air passing through the paper per unit time While a'constant differential pressure is applied across the paper. Tensile strength and tearing strength bear some relationship to the stress the paper undergoes inservice, and therefore these properties are also determined. Also the well-known pick test is significant for all papers to be printed. The results of the foldingendurance tests on the paper treated in accordance with the presentinvention are set out in Table 2. Also set out in this table are the changes in the folding endurance produced by varying the precentages of the resin and the plasticizer in the bath. It will be noted that when the resin was reduced from to 8 percent, the folding endurance in the machine direction decreased by a factor of approximately one-quarter. When the resin was used and no'plasticizer was added the folding endurance was almost the same as that of the control (i.e., untreated) paper.

In Table 3 the effects of the temperature at which the paper is dried maybe seen. This table indicates the results of the various tests to which the paper was subjected. It'will be noted that when the paper was dried at 105 degrees centigrade, there was a substantial increase in the folding endurance of the paper, an increase in 'the tensile strength, and a decrease in the air permeability after crumpling. Specifically, the folding-endurance properties of the rag paper were increased by a factor of 1500 percent and the air permeability of the paper after 24-cycle crumpling procedure on a National Bureau of Standards tester was reduced by a factor of 6. The tensile strength of the paper increased by a factor of approximately percent.

TABLE 3 Effect of treatment on properties of currency paper Currency Sized with Solution A Unsized Currency Dried at Dried at Basis weight (25 x 40-500) (lb.)- 56. 3 65. 5 65.5 Thickness (in.) 0035 .0041 .0039 MIT Fold, double folds:

Machine Direction 2, 300 5, 816 40, 000

Cross Direction 1, 500 4, 589 20, 000 Tensile strength (10./15 mm Machine direction..- 23 23.1 31

Cross Direction, 12 12. 4 l6 Elongation (percent):

Machine direction 2. 5 4. 3 4. 3

Cross directivnu 8. 3 10. 5. 10.5 Oil Penetration (sec) 1, 470 Oil does not penetrate Pick: withstands Denni on Wax No 12 16 16 Air permeability after 24 cycles of crumpling (c.s.m.) 240 112 40 hand the oil penetration of types .of papers.

this paper is practically all. This is very important considering the amount of natural oils from the skin of users that will rub off on the paper, thereby adversely afiecting its durability.

The above results were obtained with rag paper. However, reference to Table 4 will show that this treatment is not limited to rag paper but may be used also with other The results shown in Table 4 were obtained with wood-fiber papers.

TABLE 4 Efiect of treatment on properties of wood-fiber papers Tensile MIT Folding Strength, Endurance, Sample No. lb./15 n1n1. 1 kg. tension M.D. O.D. M.D. O.D.

Before 9.0 4. 7 1, 700 1, 761 1133After 20.2 12.0 6,000+ 3, 000+ Before-.- 7.6 4.6 2, 800 1,200 Afton-.- 10.0 6.1 6,000+ 13, 000+ Sample 1167 was purified wood pulp with 10.8 percent clay filler; 1133 was 50 percent soda pulp and .50 percent sulfite pulp with no filler. The drying temperature was 60 degrees centigrade. l

The above discussion and tables have related to the use of glycerol in the sizing solution. The improvement obtained by using sorbitol or mannitol as the plasticizer was not as marked as that obtained when glycerol was used. However, there was a definite increase in the tensile strength of the paper Without a reduction in any of the other properties.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made within the scope of my invention as defined in the appended claims.

I claim:

1. A method for treating fibrous cellulose materials which comprises immersing the material in a bath consisting essentially of 15-20 percent by weight of a water soluble polyhydric alcohol selected from the group consisting of glycerol, mannitol, and sorbitol, 10-15 percent by weight of urea-formaldehyde resin, and the remainder water, and drying the material at a temperature of .at least 60 degrees centigrade.

2. A method of treating paper which comprises immersing the paper in a bath consisting essentially of 15- 20 percent by weight glycerol, 10-15 percent by weight urea-formaldehyde resin, and the remainder water, and drying the material at a temperature of at least 60 degrees centigrade.

3. A method of treating paper which comprises immersing the paper in a bath consisting essentially of 15- 20 percent by weight glycerol, 10-15 percent by weight urea-formaldehyde resin, and the remainder water, and drying the material at degrees centigrade.

4. A fibrous cellulose material with a plastic material formed between the fibers, said plastic material consisting essentially of urea-formaldehyde resin and a polyhydric alcohol selected from the group consisting of glycerol, mannitol, and sorbitol, said urea-formaldehyde resin comprising 3-4 percent of the total weight of said material, and said alcohol comprising 7-9 percent of the total weight of said material.

5. A fibrous cellulose material with a plastic material formed between the fibers, said plastic material consisting essentially of urea-formaldehyde resin and glycerol, said urea-formaldehyde resin comprising 3-4 percent of the total weight of said material and. said glycerol comprising 7 -9 percent .of the total weight of said material.

6. A tub-sizing bath for fibrous cellulose materials, consisting essentially of 15-20 percent by Weight of a 5 water-soluble polyhydric alcohol selected from the group consisting of glycerol, mannitol, and sorbitol, 10-15 percent by weight of urea-formaldehyde resin, and the remainder water.

7. A tub-sizing bath for fibrous cellulose materials consisting essentially of 15-20 percent by weight glycerol, 10-15 percent by weight urea-formaldehyde resin, and the remainder water.

References Cited in the file of this patent UNITED STATES PATENTS Goepp Mar. 22, 1938 Pollard Mar. 4, 1947 Pollard Aug. 21, 1951 Nielsen May 13, 1952 Berry et a1. July 27, 1954 Rosser Jan. 11, 1955 

1. A METHOD FOR TREATING FIBROUS CELLULOSE MATERIALS WHICH COMPRISES IMMERSING THE MATERIAL IN A BATH CONSISTING ESSENTIALLY OF 15-20 PERCENT BY WEIGHT OF A WATERSOLUBLE POLYHYDRIC ALCOHOL SELECTED FROM THE GROUP CONSISTING OF GLYCEROL, MANNITOL, AND SORBITOL, 10-15 PERCENT BY WEIGHT UREA-FORMALDEHYDE RESIN, AND THE REMAINDER WATER, AND DRYING THE MATERIAL AT A TEMPERATURE OF AT LEAST 60 DEGREES CENTIGRADE. 